Phenylglyoxalic Esters Generating by Photolysis Low Migratable Fragments

ABSTRACT

The present invention concerns photopolymerisable systems comprising reactive oligomers and/or monomers having ethylenically unsaturated groups and at least one phenylglyoxalic ester that, by photochemical decomposition, generates fragments having low migratability and low odour.

This invention concerns photopolymerisable systems containingphenylglyoxalic esters that, by photochemical decomposition, generatefragments having low migratability and low odour.

Photopolymerisable systems contain photoinitiators characterised by thepresence within their molecule of a functional group that, byelectromagnetic excitation, generally UV radiation, generates radicalsthat are able to start a polymerisation process.

As it is known, both the photoinitiators and the fragments deriving fromphotochemical decomposition during the polymerisation process mustfollow strict criteria of low toxicity, volatility, migratability andodour and must be highly compatible within the photopolymerisablesystem.

These characteristics are essential particularly in the field of foodpackaging coating.

Aromatic phenylglyoxalic esters and their use as photoinitiators areknown and described, for example, in U.S. Pat. No. 4,038,164, U.S. Pat.No. 4,024,297 and U.S. Pat. No. 4,475,999.

More recently, in U.S. Pat. No. 6,048,660, a large family ofphenylglyoxalic esters is described; they are said to possess lowvolatility and low odour, but it is not reported if such characteristicscan also be found in the products originating from theirphoto-decomposition.

The products originating from the decomposition of the phenylglyoxalicesters of U.S. Pat. No. 6,048,660, nonetheless, derive from the radicalsR₁CO and R₂CO; in the simplest cases, these radicals becomebenzaldehyde, 4-methoxy-benzaldehyde, 4-methylthio-benzaldehyde, etc. .. . which are notoriously irritant and malodorous.

We have now found that the members of a restricted family of aromaticphenylglyoxalic esters having formula I:

wherein

A is selected among O, S, NR₃, linear or branched C₁-C₆ alkyl orcycloalkyl and R₃ is hydrogen or C₁-C₆ linear or branched alkyl;

R₁ and R₂ are, independently of one another, linear or branched C₁-C₁₈alkyl or cycloalkyl, (CH₂CH₂O)_(n)R₄ where n is a number from 1 to 6 andR₄ is hydrogen or linear or branched C₁-C₄ alkyl, or CH₂CH₂N(R₅)₂ whereR₅ is linear or branched C₁-C₄ alkyl,

by photochemical decomposition, generate fragments having lowmigratability, volatility and odour.

The photopolymerisable systems comprising reactive oligomers and/ormonomers having ethylenically unsaturated groups and, asphotoinitiators, the phenylglyoxalic esters of formula I are afundamental object of the present invention, and are particularly usefulfor the preparation of coatings for food packaging.

Among the products which are particularly useful for the realisation ofthe present invention we cite the compounds of formula I wherein A isselected among O, S or CH₂, and R₁ and R₂ are methyl, ethyl, i-propyl,n-propyl, n-butyl, i-butyl, t-butyl, or CH₂CH₂OR₄ where R₄ is hydrogen,methyl or ethyl; the preferred products are those having formula Ia-Ie:

The phenylglyoxalic esters of formula I of the present invention may beprepared by conventional methods which are well known to the man skilledin the art.

In particular, it is possible to carry out a Friedel Crafts reactionbetween

where A is selected among O, S, NR₃, linear or branched C₁-C₆ alkyl orcycloalkyl and R₃ is hydrogen or linear or branched C₂-C₆ alkyl, andmethyl oxalyl chloride and optionally transesterifiying the obtainedproduct with R₁OH and/or R₂OH, where R₁ and R₂ are, independently of oneanother, linear or branched C₂-C₁₈ alkyl or cycloalkyl, (CH₂CH₂O)_(n)R₄where n is a number from 1 to 6 and R₄ is hydrogen or linear or branchedC₁-C₄ alkyl, or CH₂CH₂N(R₅)₂ where R₅ is linear or branched C₁-C₄ alkyl,in the presence of a transesterification catalyst.

It is a further object of the present invention a process for therealisation of coatings for metal, wood, paper or plastic surfaces,comprising applying the photopolymerisable system comprising reactiveoligomers and/or monomers having ethylenically unsaturated groups and atleast one phenylglyoxalic esters of formula I, and preferably of formulaIa, Ib, Ic, Id, or Ie, to obtain, after polymerisation, a 0.5 to 100microns thick coating, and subsequently photopolymerising with a lightsource having emission bands in the UV-visible region and up to 450 nm.

The term “photopolymerisation” is intended in a wide sense and include,for example, the polymerisation or crosslinking of polymeric materials,such as for example pre-polymers, the homopolymerisation and thecopolymerisation of simple monomers and the combination of this kind ofreactions.

Monomers useful in the described system include, for example:acrylonitrile, acrylamide and its derivatives, vinyl ethers,N-vinylpyrrolidone, mono and polyfunctional allyl ethers, such as forexample trimethylolpropane diallylether, styrenes and alpha-methylstyrenes, esters of acrylic and methacrylic acid with alyphaticalcohols, with glycols, or with polyhydroxylated compounds, as forexample pentaerythritol, trimethylolpropane or aminoalcohols, esters ofvinyl alcohol with aliphatic or acrylic acids, derivatives of fumaric ormaleic acid.

The oligomers which are useful for the present invention include, forexample, polyesters, polyacrylates, polyurethanes, epoxidic resins,polyethers with acrylic, maleic or fumaric functionalities.

Compounds of formula I of the present invention acts as photoinitiatorsand can be used alone or in combination with other photoinitiators asfor example benzophenone and its derivatives (such asmethylbenzophenone, trimethylbenzophenone), acetophenone derivatives,such as for example α-hydroxyacetophenones, (asα-hydroxycyclohexylphenyl ketone,oligo-[2-hydroxy-2-methyl-1-[4-(1-methylvinyl)phenyl]-propanone],2-hydroxy-2-methyl-1-phenyl-propanone,2-hydroxy-1-[4-(2-hydroxy-ethoxy)-phenyl]-2-methyl-propan-1-one,1-[2,3-dihydro-1-[4-(2-hydroxy-2-methyl-1-oxopropyl)phenyl]-1,3,3-trimethyl-1H-inden-5-yl]-2-hydroxy-2-methyl-1-propanone,1-[2,3-dihydro-3-[4-(2-hydroxy-2-methyl-1-oxopropyl)phenyl]-1,1,3-trimethyl-1H-inden-5-il]-2-hydroxy-2-methyl-1-propanone,4,3′-bis(α,α-hydroxy-isobutyryl)-diphenylmethane,4,4′-bis(α,α-hydroxy-isobutyryl)-diphenylmethane,4,3′-bis(α,α-hydroxy-isobutyryl)-diphenylether,4,4′-bis(α,α-hydroxy-isobutyryl)-diphenylether), α-aminoacetophenones(as2-dimethylamino-2-(4-methylbenzyl)-1-(4-morpholin-4-yl-phenyl)-butan-1-one,2-benzyl-2-dimethylamino-1-(3,4-dimethoxy-phenyl)-butan-1-one,2-benzyl-2-dimethylamino-1-(4-morpholin-4-yl-phenyl)-butan-1-one,2-methyl-1-(4-methylsulfanyl-phenyl)-2-morpholin-4-yl-propan-1-one),ketosulfones (as1-[4-(4-benzoyl-phenylsulfanyl)-phenyl]-2-methyl-2-(toluene-4-sulfonyl)-propan-1-one),dialcoxyacetophenones, benzoin ethers, benzyl ketals (as benzyl dimethylketal), phenylglyoxylic acid esters and their derivatives (asphenylglyoxylic acid methyl ester, ethyl ester of2-(2-oxo-2-phenyl-acetoxy-etoxyethyl)oxyphenylacetic acid),monoacylphosphine oxides, as (2,4,6-trimethylbenzoyl)-diphenyl-phosphineoxide or the ethyl ester of phenyl-(2,4,6-trimethylbenzoyl)-phosphinicacid, bisacylphosphine oxides, (asbis-(2,6-dimethoxybenzoyl)-(2,4,4-trimethyl-pent-1-yl)phosphine oxide,bis(2,4,6-trimethyl benzoyl)-phenyl-phosphine oxide,bis(2,4,6-trimethylbenzoyl)-(2,4-dipentoxyphenyl)phosphine oxide),trisacylphosphine oxides, halogenomethyltriazine, ferrocene ortitanocene derivatives, photoinitiators containing the borate orO-acyloximic group, sulphonium, phosphonium or iodonium aromatic salts.

In addition to the compounds of formula I, many other components may beincluded in the photopolymerisable systems of the invention, for examplethermal stabilisers, sensitisers, photo-oxydation stabilisers such assterically hindered amines, antioxidants, oxygen inhibitors, thermalradicals generators such as organic and inorganic peroxides, peresters,hydroperoxides, benzopinacols, azoderivatives such asazodiisobutyronitrile, metallic compounds such as cobalt(II) salts,manganese, antifoams, fillers, dispersing agents, pigments, dyes and/ormatting agents, other additives of general use, dispersed solids, glassand carbon fibres, thixotropic agents.

Chemically inert non photopolymerisable polymers, as for examplenitrocellulose, polyacrylic esters, polyolefines etc., or polymers whichare crosslinkables with other systems, as for example with peroxides andatmospheric oxygen or acid catalysis or thermal activation, as forexample polyisocyanates, urea, melamine or epoxidic resins are furthercomponents that may be included in the photopolymerisable systems.

The compounds of formula I are generally used in the photopolymerisablesystem in quantity of 0.01 to 20% by weight, preferably of 1 to 6% byweight, on the total weight of the photopolymerisable system and areperfectly compatible with the system, imparting to it high photochemicalreactivity and heat stability.

The compounds of formula I are very efficient photoinitiators both inclear and in pigmented photopolymerisable systems and are useful forexample for the preparation of photocrosslinkable inks. They areespecially suited for use in the coating of PVC floor and in theautomobile field.

Examples of sources of light useful for the photopolymerisation of thephotopolymerisable systems prepared according to the invention aremercury vapour or superactinic or excimers lamps, with emission bands inthe UV-visible region and particularly between 180 and 450 nm.

Among the useful sources of light, sunlight and other artificial sourcesemitting electromagnetic radiation with a wavelength from 180 nm up tothe IR region are also included.

A further advantage of the present invention is the fact that, usingstarting compounds which are easily available on the market, by varyingthe group

A in formula I, it is possible to modify the absorbance spectrum of thephenyglyoxalic ester so to increase its reactivity in pigmented systems.

The phenylglyoxalic esters of the present invention have a highreactivity, as shown in the application tests here reported; beside notgenerating benzaldehyde or substituted benzaldehyde, they are themselveslow migratable, low volatile and low odorous.

Examples of the preparation of compounds of formula I and ofphotopolymerisable systems containing them are herein reported, not tolimit but to illustrate the invention.

EXAMPLE 1 Synthesis of [4-(4-Methoxyoxalyl-phenoxy)-phenyl]-oxo-aceticacid methyl ester (Ia)

31.3 g (0.235 mol) of AlCl₃ were added in 30′, under stirring and inportions, to a solution of 10 g (0.0587 mol) of diphenylether and 11.33ml (0.123 mol) of methyl oxalyl chloride in 300 ml of dichloromethane,at a temperature of 0 to 5° C.

At the end of the addition the temperature was raised to roomtemperature and after three hours the reaction was completed. Thereaction mixture was poured into a solution of 200 ml of water and iceacidified with 15 ml of concentrated HCl. The organic phase wasseparated, washed twice with brine, dried on sodium sulphate, andevaporated under vacuum. The oily residue, taken with 100 ml ofpetroleum ether, solidified.

17.4 g of product Ia were obtained (yield 87%).

¹HNMR, 300 MHz, CDCl₃ δ(ppm): 8.10, m, 4H; 7.12, m, 4H; 3.98, s, 6H

EXAMPLE 2 Synthesis of [4-(4-Methoxyoxalyl-benzyl)-phenyl]-oxo-aceticacid methyl ester (Ib)

5.33 g (0.04 mol) of AlCl₃ were added in one portion, under stirring atroom temperature, to a solution of 1.68 g (0.01 mol) of diphenylmethaneand 1.93 ml (0.021 mol) of methyl oxalyl chloride in 100 ml ofdichloromethane.

After four hours the reaction was completed. The reaction mixture waspoured into a solution of 100 ml of water and ice acidified with 2.5 mlof conc. HCl. The organic phase was separated, washed twice with brine,dried on sodium sulphate, and evaporated under vacuum. The oily residuewas washed with petroleum ether and then evaporated.

3.2 g of product Ib were obtained as a yellow oil (yield 94%).

¹H-NMR, 300 MHz, CDCl₃ δ(ppm): 8.10, m, 4H; 7.32, m, 4H; 4.15, s, 2H;3.98, s, 6H

EXAMPLE 3 Synthesis of[4-(4-Methoxyoxalyl-phenylsulfanyl)-phenyl]-oxo-acetic acid methyl ester(Ic)

7.14 g (0.0536 mol) of AlCl₃ were added in one portion, under stirringat room temperature, to a solution of 2.5 g (0.0134 mol) ofdiphenylsulphide and 2.58 ml (0.0281 mol) of methyl oxalyl chloride in100 ml of dichloromethane. A sticky precipitated product was formed.

100 ml of dichloromethane were added and the mixture was left overnightat r.t.

The reaction mixture was poured into a solution of 200 ml of water andice acidified with 3.5 ml of conc. HCl. The organic phase was separated,washed twice with brine, dried on sodium sulphate, and evaporated undervacuum. The oily residue was washed with petroleum ether and thenevaporated.

5 g of product were obtained as an oil.

The product was purified by flash chromatography eluting withdichloromethane/petroleum ether 7/3 and then with dichloromethane.

The residue solidified in petroleum ether and was filtrated; 850 mg ofproduct Ic were obtained.

¹H-NMR, 300 MHz, CDCl₃ δppm): 8.01, m, 4H; 7.49, m, 4H; 3.98, s, 6H.

EXAMPLE 4 Synthesis of [4-(4-Butoxyoxalyl-phenoxy)-phenyl]-oxo-aceticacid butyl ester (Id)

50.5 mg (0.2 mmol) of dibutyltin oxide were added to a suspension of 2 gof product Ia in 10 ml of n-butanol. The reaction was heated underreflux and a solution obtained. After two hours the reaction wascompleted. The solution was diluted with 100 ml of dichloromethane andthe organic phase washed twice with water, dried on sodium sulphate, andevaporated under vacuum to give an oily product which was purified byflash chromatography eluting with petroleum ether/dichloromethane 1/1.

1.6 g of product Id were obtained as a yellow oil.

¹H-NMR, 300 MHz, CDCl₃ δ(ppm): 8.1, m, 4H; 7.15, m, 4H; 4.4, t, 4H;1.78, m, 4H; 1.45, m, 4H; 0.9, t, 6H

EXAMPLE 5 Synthesis of{4-[4-(2-Methoxy-ethoxyoxalyl)-phenoxy]-phenyl}-oxo-acetic acid2-methoxy-ethyl ester (Ie)

50.5 mg (0.2 mmol) of dibutyltin oxide were added to a suspension of 2 gof product Ia in 10 ml of 2-methoxyethanol. The reaction was heatedunder reflux and a solution obtained. After two hours the reaction wascompleted. The solution was diluted with 100 ml of dichloromethane andthe organic phase washed twice with water, dried on sodium sulphate, andevaporated under vacuum to give an oily product which was purified byflash chromatography eluting with petroleum ether/ethyl acetate 6/4.

730 mg of product Ie were obtained as a yellowish oil.

¹H-NMR, 300 MHz, CDCl₃ δ(ppm):): 8.1, m, 4H; 7.15, m, 4H; 4.55 μm, 4H;3.73, m, 4H; 3.41, s, 6H.

Application Tests.

The substances used for the preparation of the photopolymerisablesystems evaluated in the following applicative tests are:

Ebecryl (R)284 (aliphatic urethane acrylate from UCB, Belgium);

TPGDA (tripropylene glycol diacrylate)

TMPTA (trimethylolpropane triacrylate).

As photoinitiators, the compounds Ia-Ie of Examples 1-5 were used:

For the evaluation of the photopolymerisable systems, two matrixes wereprepared mixing (% w/w), for the first matrix Ml:

Ebecryl 284 (R) 70% TMPTA 15% TPGDA 15%

for the second matrix M2:

Ebecryl 284 (R) 75% TPGDA 25%

The photopolymerisable systems to be evaluated are then prepared withthe compositions reported in Table 1.

TABLE 1 Photopolymerisable systems composition (% w/w) A B C D E FMatrix M1 95 Matrix M2 96 96 96 96 96 Compound Ia 5 4 Compound Ib 4Compound Ic 4 Compound Id 4 Compound Ie 4

The evaluation of the photopolymerisable systems was done by determiningthe reactivity, through cure and yellow and white indexes.

Reactivity.

The photopolymerisable system is laid with a thickness of 50 or 6microns on a varnished cardboard using a bar-coater mounted on anelectric stretch-film and thereafter irradiated at a distance of 26 cmfrom the light source. A Fusion(R) photopolymerisator was used, equippedwith a medium pressure mercury lamp operating with about 50% of itsnominal power (about 120 W/cm).

The photopolymerisation speed, measured in m/min, is the maximumpossible speed that results in a perfect superficial crosslinking of thesystem (“tack free”).

The maximum speed (expressed in m/min) resulting in a surface resistantto any visible damage after rubbing with abrasive paper was alsomeasured (superficial abrasion).

The greater is the maximum speed, the greater is the efficiency of thesystem.

The obtained results are reported in Table 2.

TABLE 2 A B C E D F Tack-free (m/min) 50 μm 45 41    36.5 32 28 27Tack-free (m/min) 6 μm 43.5 — — — — — Superficial abrasion 10 10**  10***   10***  5  4 (m/min) 50 μm **two passages ***three passages

White and Yellow index

The photopolymerisable system is laid with a thickness of 100 μm on avarnished cardboard using a bar-coater mounted on an electricstretch-film and then is passed at a distance of 26 cm from the lightsource, at a speed corresponding to 70% of the tack-free speed. AFusion(R) photopolymerisator was used, equipped with a medium pressuremercury lamp operating with about 50% of its nominal power (about 120W/cm).

White and yellow indexes were measured according to ASTM D1925-70standard test method. A low value of yellow index and a high value ofwhite index correspond to high stability of the colour of theformulation.

The results are reported in Table 3.

TABLE 3 A B C E D F Yellow 6.6 6.8 9.2 12.0 — — Index White Index 66.766.1 60.3 53.4 — —

Odour Evaluation.

The photopolymerised systems B-F and a system prepared by mixing 4 partsby weight of Esacure (R)KL200 (hydroxyketone sold by Lamberti SpA) and96 parts by weight of matrix M2 (photopolymerisable system G) are laidwith a thickness of 50 μm on a varnished cardboard using a bar-coatermounted on an electric stretch-film and then is passed at a distance of26 cm from the light source, at a speed corresponding to 70% of thetack-free speed. A Fusion(R) photopolymerisator was used, equipped witha medium pressure mercury operating with about 50% of its nominal power(about 120 W/cm).

The samples are photopolymerised to obtain a perfect crosslinking(“tack-free”).

The thus obtained cardboard samples are put into closed glass jars andthe jars are stored in oven for 30 minutes at 60° C.

Three people, independently of one another, evaluate the odour of thesamples, rating each photopolymerised system for odour intensity on thefollowing scale:

No odour 0 Very slight odour 1 Slight odour 2 Intense odour 3 Veryintense odour 4

The odour evaluations (average of three ratings) are reported in Table4.

TABLE 4 A B C E D F Odour intensity 1.3 2.0 2.6 1.6 1.6 3.3

1-10. (canceled)
 11. A photopolymerizable system comprising at least onephenyl glyoxalic ester photoinitiator having the general formula I:

wherein: A is selected from the group consisting of O, S, NR₃, a linearor branched C₁-C₆ alkyl or cycloalkyl and R₃ is hydrogen or a C₁-C₆linear or branched alkyl; and R₁ and R₂ are, independently of oneanother, selected from the group consisting of: a linear or branchedC₁-C₁₈ alkyl or cycloalkyl, (CH₂CH₂O)_(n)R₄ where n is a integer from 1to 6 and R₄ is hydrogen or a linear or a branched C₁-C₄ alkyl, andCH₂CH₂N(R₅)₂ where R₅ is a linear or branched C₁-C₄ alkyl.
 12. Thephotopolymerizable system of claim 11 wherein: A is selected from thegroup consisting of: O, S or CH₂; and R₁ and R₂ are, independently ofone another, selected from the group consisting of: methyl, ethyl,i-propyl, n-propyl, n-butyl, i-butyl, t-butyl, and CH₂CH₂OR₄ where R₄ ishydrogen, methyl or ethyl.
 13. The photopolymerizable system of claim 12wherein the phenyl glyoxalic ester has a formula selected from the groupconsisting of:


14. The photopolymerizable system of claim 11 further comprising anadditional photoinitiator.
 15. The photopolymerizable system of claim 14wherein the additional photoinitiator is a benzophenone photoinitiator.16. The photopolymerizable system of claim 14 wherein the additionalphotoinitiator is an α-hydroxyacetophenone photoinitiator.
 17. Thephotopolymerizable system of claim 14 wherein the additionalphotoinitiator is a ketosulfone photoinitiator.
 18. Thephotopolymerizable system of claim 14 wherein the additionalphotoinitiator is a phenyl glyoxilic acid ester photoinitiator.
 19. Thephotopolymerizable system of claim 4 wherein the additionalphotoinitiator is selected from the group consisting ofacylphosphineoxide photoinitiators; borate photoinitiators; O-acyloximicphotoinitiators; sulphonium aromatic salt photoinitiators; phosphoniumaromatic salt photoinitiators; iodonium aromatic salt photoinitiators;halogenomethyltriazine photoinitiators; ferrocene photoinitiators;titanocene photoinitiators: and mixtures thereof.
 20. Thephotopolymerizable system of claim 1 additionally comprising at leastmember selected from the group consisting of thermal stabilisers,sensitizers, photo-oxidation stabilisers, thermal radicals generators,antifoams, fillers, dispersing agents, pigments, dyes, matting agents,dispersed solids, glass fibers, carbon fibers, thixotropic agents,chemically inert non photopolymerizable polymers, crosslinkablepolymers, and mixtures thereof.
 21. The photopolymerizable system ofclaim 11 wherein the phenyl glyoxalic ester is present at aconcentration of from about 0.01 to 20 percent by weight.
 22. Thephotopolymerizable system of claim 11 wherein the phenyl glyoxalic esteris present at a concentration of from about 1 to 6 percent by weight.23. The photopolylmerizable system of claim 11 wherein the at least onephenyl glyoxalic ester photoinitiator is prepared using a processincluding a Friedel Crafts reaction.
 24. A process for coating a metal,wood, paper or plastic substrate comprising: applying to the substrate aphotopolymerisable system comprising at least one phenyl glyoxalic esterphotoinitiator having the general formula I:

wherein: A is selected from the group consisting of O, S, NR₃, a linearor branched C₁-C₆ alkyl or cycloalkyl and R₃ is hydrogen or a C₁-C₆linear or branched alkyl; and R₁ and R₂ are, independently of oneanother, selected from the group consisting of: a linear or branchedC₁-C₁₈ is alkyl or cycloalkyl, (CH₂CH₂O)_(n)R₄ where n is a integer from1 to 6 and R₄ is hydrogen or a linear or a branched C₁-C₄ alkyl, andCH₂CH₂N(R₅)₂ where R₅ is a linear or branched C₁-C₄ alkyl; to obtain,after polymerisation, a coating; and photopolymerising with a lightsource.
 25. The process of claim 24 wherein the coating has a thicknessof from about 0.5 to 100 microns and the light source has a emissions inthe range of from the UV-visible region to 450 mm.
 26. The process ofclaim 24 wherein A is selected from the group consisting of: O, S orCH₂; and R₁ and R₂ are, independently of one another, selected from thegroup consisting of: methyl, ethyl, i-propyl, n-propyl, n-butyl,i-butyl, t-butyl, and CH₂CH₂OR₄ where R₄ is hydrogen, methyl or ethyl.27. The process of claim 24 wherein the phenyl glyoxalic ester isselected from the group comprising compounds having the formulas Ia, Ib,Ic, Id, and Ie.
 28. The process of claim 24 wherein the substrate issuitable for accepting inks and dyes.
 29. The process of claim 24wherein the substrate is a food wrapper.
 30. The process of claim 24wherein the substrate is polyvinyl chloride.